Abstract:

The Sanhetun gold deposit in Heilongjiang Province is located at the southwest end of the Nenjiang-Heihe tectonic melangite gold metallogenic belt. Due to the thick Quaternary overburden and insufficient deep geophysical work, the breakthrough of the deep prospecting and the research of metallogenic model are restricted. In this study, the two-dimensional electrical structure of the study area was obtained by the two-dimensional data inversion of the audio geomagnetic long profile (about 8.5 km) across the deposit using the nonlinear conjugate gradient method. The results show that the 100 m shallow layer of the Sanhetun gold deposit has the characteristics of low resistivity. It reflects the shallow Cretaceous sand-mudstone and Quaternary weathering in this area. The continuous distribution of low resistance layers and the underlying high resistance anomalies in the northwest side of the section indicates the Cretaceous volcanic rocks and Carboniferous intrusive rocks. The high and low resistance transition zones under the section reveal the deep distribution characteristics of ductile shear zones and faults. These are important ore guiding and storage structures. In this paper, the metallogenic model of the Sanhetun gold deposit is established based on the regional geological data. In the Early-Middle Jurassic tectonic extensional period, the ore-forming fluid migrated upward along the fault and ductile shear zone, and then leached the gold elements from the Late Carboniferous intrusive rocks，which contributed to the first phase of mineralization in the study area. In the Early Cretaceous, the study area was again in an extensional and pull-apart setting, and the gold elements carried by the deep magmatic eruptions were transported along the newly formed and reactivated ductile shear zones and basin margin fractures toward the edge of the Sanhetun volcanic basin with the magmatic hydrothermal fluids,and gradually precipitated and  superimposed on the top of the earlier mineralization phase with the temperature decrease in the later period.

Key words: Sanhetun gold deposit；audio magnetotellurics；electrical structure；gold metallogenic model；volcanic hydrothermal gold deposits

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Sanhetun gold deposit；audio magnetotellurics；electrical structure；gold metallogenic model；volcanic hydrothermal gold deposits

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